Method and system for determining image transformation

a technology of image transformation and method, applied in the field of image processing, can solve the problems of differential scaling, differential scaling, and significant impairing (or preventing) the detection of watermark data

Inactive Publication Date: 2005-10-25
DIGIMARC CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0007]The below-detailed technology addresses certain of the above-noted shortcomings. For example, some embodiments permit differential scaling to be discerned from an input image, together with offset, scale, and rotation. Other embodiments permit image rotation to be determined without reference to any embedded calibration signal.

Problems solved by technology

While the approach detailed in the '260 patent and its followers is satisfactory for determining offset, scale, and rotation of an input image from a reference state, it cannot discern differential scaling.
Differential scaling occurs when an image is “stretched” (or shrunk) differently in the x- and y-directions, and can significantly impair (or prevent) detection of watermark data.
If the spacing between successive rows does not precisely match the spacing between adjoining sensors, the pixels are not truly square, again resulting in differential scaling.

Method used

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Embodiment Construction

[0016]The following disclosure begins by explaining how the rotation state of a document can be discerned independently of any embedded calibration data. Once rotation state is known, this disclosure teaches how embedded calibration data—if present—can then be used to determine differential scaling.

[0017]To review briefly, many watermarking techniques change the values of certain image pixels in accordance with bits of a watermarking payload. In an exemplary watermarking system, a watermark block (e.g., of 128×128 pixels) is tiled across the original image and summed to yield the encoded image. Each pixel in the block changes an associated pixel in the image up or down in value, depending on the value of a single bit in the watermark payload.

[0018]In order to read the watermark payload from an encoded image, the detector must understand the relationship between the pixels in the image and the bits of the watermark payload to which they map. To do this, it is commonly necessary to di...

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Abstract

A watermark decoding method makes use of a line-finding algorithm (e.g., the Radon transform) to determine rotation of an image from an initial orientation. Once rotation has been characterized, differential scaling of the image can readily be determined.

Description

FIELD OF THE INVENTION[0001]The present invention relates to image processing, and more particularly relates to technologies useful in determining the offset, rotation, scale, and differential scale of an image from a reference state.BACKGROUND AND SUMMARY OF THE INVENTION[0002]In many applications, it is necessary to discern the transformation of an input image from an original state. This is the case, for example, in decoding certain digital watermarks.[0003]If the original image is available, certain image features in the original image can be matched with corresponding features in the input image so as to discern any intervening transformations. Such a system is shown in the present assignee's U.S. Pat. No. 5,930,377.[0004]If the original image is not available, other techniques must be employed. In U.S. Pat. No. 5,862,260, and in copending application Ser. No. 09 / 452,023, filed Nov. 30, 1999 (now U.S. Pat. No. 6,408,082), the present assignee detailed a system employing a subli...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): G06K9/00
CPCH04N1/32144
Inventor ALATTAR, ADNAN M.
Owner DIGIMARC CORP
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